Many electronic devices operate based on clock signals for timing various functions, for example using high frequency clock signals that are generated by an oscillator. The clock signals are ideally rectangular pulses with energy concentrated at a fundamental frequency and harmonics at the integer multiples of the fundamental frequency. Energy of the high frequency harmonics can be large enough to disturb functioning of other electronic devices through electromagnetic interference (EMI).
One technique for reducing electronic interference is to slightly vary the frequency of the clock signal, thereby spreading signal energy to a larger frequency band and reducing the contribution at any particular frequency to electromagnetic interference. The slight frequency variation can be attained through frequency or phase modulation wherein the reduction in EMI and the deviation of clock signal frequency depend on the amplitude, frequency and shape of the modulation signal.